Some exoskeleton devices may be used to assist medical patients with one or more movements. For example, exoskeleton devices may be provided for the arms or legs of a user. Where a user has full use of the limb supported by the exoskeleton device, it may be used to enhance natural abilities such as load carrying. Where the user has impaired use of the limb supported by the exoskeleton device, it may be used for rehabilitative purposes or to replicate a full physical function. Such devices may be powered by one or more motors coupled to gears or pulleys configured to move a user's limb in a desired motion, such as walking.
Some exoskeleton devices may be powered by hydraulic pumps or electric motors with planetary gear systems. However, the hydraulic components may leak and require a vent valve. The electric motors with planetary gear systems may have high friction which makes it difficult to back-drive, and may have lash that results in noise and poor user feel during operation. Accordingly, it is desirable to provide new methods to power exoskeleton devices.